The most dangerous sex offenders will be forced to take regular lie detector tests after leaving jail in a bid to prevent fresh attacks.

After a successful trial was carried out in the Midlands, ministers are now set to introduce compulsory lie detector tests across England and Wales in 2014.

Experts will grill the 750 worst offenders about their activities and intentions to try to discover if they are plotting new crimes.

Tests: No10 wants mandatory tests for all high
risk sex offenders - such as nursery school paedophile Vanessa George, left, and
child killer Jon Venables, right, after a successful trial in the Midlands
between 2009 and 2011

This is expected to include criminals
such as child murderer Jon Venables and nursery paedophile Vanessa
George, who will be hooked up to monitors every three months.

Lie detectors, known as polygraph
machines, measure a person’s pulse, blood pressure and breathing rate.
An electronic graph plots these rates as questions are asked, and
involuntary changes in the body can indicate whether a person is telling
the truth or not.

During the pilot scheme, sex offenders
attached to lie detectors made twice as many admissions to breaches of
their probation conditions compared to those questioned without the
machines.

THE TRUTH ABOUT LIE DETECTORS

Polygraphs are used routinely by police in the U.S. but are considered too unreliable for use in criminal trials in the UK. It is disputed as to how accurate they are.

Until now they have been mostly used on television to settle domestic disputes.

A polygraph measures and records blood pressure, pulse and breathing while the subject is asked a series of questions.

It takes about two hours to complete three different phases. The first is the pre test interview, where the examiner explains the test. The subject is then attached to the polygraph and a set of questions asked several times.

Once the data has been collected it is analysed in stage three and the results are announced. Examiners say nerves should not affect the results.

Deceptive answers produce physiological responses that are different to truthful answers.

The machine was invented in 1921 by John Augustus Larson at the University of California at Berkeley alongside a police officer.

One freed rapist was returned to jail
after admitting he had been performing sex acts in public.

In another
case, a paedophile confessed he had started dating a woman, leading
investigators to discover he had been undressing in front of her young
daughter.

Psychiatrist Don Grubin, who helped
run the Midlands trial, said: ‘I have no doubt that serious offences
have been prevented through use of this technology.’

The Government hopes to have the
£4,000 polygraph machines - which monitor a person's heart rate,
breathing and blood pressure - up and running by 2014.

Probation minister Crispin Blunt said: 'Protecting the public from dangerous and violent offenders is a crucial part of offender management and I am committed to helping probation officers stop these offenders committing further crime and creating more victims and more misery.

'The recent pilots into using lie detector tests to manage sex offenders in the community has proved a clear success and we are now considering how we will use them across England and Wales subject to Parliamentary approval.

'This will be good news for the public who should benefit from this extra layer of protection.'

The pilot scheme in the Midlands, run by the Ministry of Justice, found that the lie detector tests led to offenders being more honest with their probation officers.

They made twice as many disclosures to staff as those who were quizzed without the polygraphs.

Their
revelations included admitting to contacting a victim or entering an
exclusion zone. Some confessed to fantasies, suggesting they would
offend again.

Offenders also reported that the tests helped them to manage their own behaviour better.

The
lie detector tests would be on top of other rigorous conditions that
sex offenders face once they have served their prison sentences.

These
include signing the sex offenders’ register, restrictions on where they
live and being banned from entering certain areas or coming into
contact with potential victims.

The tests were carried out between April 2009 and October 2011 in the East and West Midlands probation regions.

There are around 3,000 sex offenders
on licence in the community at any time, with more than 750 considered
to be the most serious cases.

Jail: Anyone who fails the test could be recalled to prison or have their parole conditions changed. The lie detector tests a person's blood pressure, heart rate and breathing and could be in place by 2014

The
compulsory use of lie detectors was challenged under human rights
legislation but judges backed the use of polygraphs, saying that they
were ‘proportionate’.